Taking these up in alphabetical order, we have first of all bronze green, but as this is a color that artists will prefer to mix themselves, we may pass it by, because when wanted by sign writers or decorators, the manufacturer can fill it into collapsible tubes from such stock as he may quote in his oil color list. The same applies to what we know as chrome green.
Cinnabar Green is a misnamed pigment, as when cinnabar is referred to the first thought leads to vermilion or red, but it is a color recognized by artists and usually furnished in collapsible tubes in three shades, light, medium and dark. The most permanent cinnabar green is made by mixing Guignet's (chromium oxide hydrate) green with cadmium yellow and the next in permanency, a mixture of Guignet's green and zinc yellow. Most fugitive are so-called cinnabar greens that are made of mixtures of Prussian blue and yellow lake or gamboge. To ascertain whether cinnabar green is made from Guignet's green and cadmium yellow the pigment is extracted in the usual way and treated with a solution of lye. If the pigment is a mixture of Prussian blue and chrome yellow, yellow lake or gamboge, the yellows are extracted by the solution and the blue changed to hydrated iron oxide, while if Guignet's green is present, it will have suffered no change. To produce a medium shade of best quality of cinnabar green, mix five parts by weight of Guignet's green, two parts normal cadmium yellow (cadmium sulphide) and three parts of poppyseed oil, and grind this mixing in a clean stone mill of a size apportionate to the batch until inpalpably fine. Avoid contact with copper or iron as much as possible. For a darker shade, use more green, for a lighter shade more cadmium yellow.
Emerald Green in the list of artists' colors is what appears in commercial color lists as Paris green with this difference, that here the pigment selected is that imported from France and that it is ground in poppyseed or nut oil in place of linseed oil. All the remarks previously made about this pigment apply here.
Color manufacturers in Europe are using any number of fantastical names for this green, because of the reluctance of consumers to purchasing or using it under its original name of Schweinfurt or Paris green. It is sold as opaque, mitis, patent, meadow, Vienna, Leipsic and parrot green. Vert Paul Veronese green is also identical with Paris green. Eighty-five Parts by weight of French pale Paris green and fifteen parts of clarified poppyseed oil is the proper proportion for mixing, although it may be necessary to use a little more oil.
Emeraude Green, also known as vert emeraude in France and as viridian in England, while the German term is smaragd green, is a very pretty, rich green pigment of fine transparency and great permanency, because it is unaffected by dilute acids and alkalies, as well as by sulphuretted hydrogen. Commonly known as Guignet's green, it is the hydrated oxide of chromium green and sixty-five parts by weight of the dry pigment and thirty-five parts by weight of poppyseed or nut oil, make when ground fine in a suitable stone mill, an excellent product for the artist. It is not customary to label this color Guignet's green. The color grinder can test this pigment in the regular way in comparison with other samples, but to be certain of his ground, he should make the dilute acid and alkali test, as there are so-called permanent greens in the market that are intimated to be chromium oxide greens, when in fact, they are merely made from organic dyes.
Oxide of Chromium Green, when so-called, must differ from emeraude green, as this is an opaque pigment, while the latter is transparent. The chrome oxide green is rather olive in color as against the deep rich green of the hydrated chrome oxide, but is even more permanent than the latter, as the strongest degrees of heat will not alter it, while the latter under such heat will lose its water of hydration and return to the olive toned chrome oxide green. This pigment, however, can be purchased at one-third the market price of Guignet's green. Seventy-five parts of the dry pigment and twenty-five parts by weight of poppyseed or nut oil make a good paste for collapsible tubes. The dry green is highly valued for coloring soap and high-grade paper and because of resistance to very high degrees of heat it is invaluable for use in the ceramic art and in enameling, etc.
Sap Green does not work very well as an oil color, yet it is in moderate demand in the line of artists' tubes. Artists use it as a glaze to obtain certain effects, such as for instance, the leaves of trees in an autumn scene picture. This green is usually made of Prussian blue and yellow lake or Dutch pink of the better grade; when one part of the blue to three parts French yellow lake, ground in four parts poppyseed oil produces a far better, but more expensive green than one part blue and nine parts Dutch pink in five parts poppyseed oil. A far better sap green would be produced, however, for the artists' purpose by a grinding of six parts Guignet's green, two parts super French yellow lake in five parts poppyseed oil, which will prove most expensive of the formulas here given, but also most permanent and best working as an oil color.
Terre Verte or Verona Green. This is natural green earth found in the rocks near the town of Verona in the north of Italy. The pigment most acceptable to the use of artists is that found in that vicinity, the Bohemian green earth and that in the United States being too grayish. Terre verte derives its color from ferric oxide and ferrous oxide, that has a gangue of silica with very small portions of alumina and larger percentages of potash, magnesia and soda. For the guidance of the color grinder we will say that the best specimens of natural green earth that are available for the use of the artist, are of a deep grayish green color, that when treated with alkalies or acids, must not show any reaction or changes in color. When a sample of green earth in powdered form is treated with dilute sulphuric or hydrochloric acid, then washed and filtered, dried and mixed with oil, it must show no appreciable change in color when a portion of the original specimen is mixed with oil and placed alongside of it on a strip of clear glass for comparison. A specimen of green earth that shows up a rich, deep green should be viewed with suspicion and a sample placed in a test tube with absolute alcohol in order to ascertain whether it has not been enriched with a green of coal-tar origin. If such is not the case, the sample should be tested for the presence of Prussian blue by treating it with a solution of caustic soda, which will destroy the blue, if any be present. Terre verte of the highest grade is very rare and very little of it comes to this country, as it is eagerly taken up by the European color manufacturers and the very best selection ever handled by the writer, was quoted by Italian exporters at a figure of $220 per long ton, f. o. b. Leghorn. Specimens of green earth, quoted anywhere from $65 to $115 per ton, were found to be enriched by either Prussian blue or aniline green, while the ordinary green earths, that can be purchased at anywhere from $25 to $45 per ton, cannot be considered at all in reference to artists' color, and at best would pass only as fillers for bronze or olive greens. Bohemian green earth and the green earths found in the United States belong to this class.
To grind the best grade of green earth referred to for use on the palette of the artist, mix sixty-eight parts of the dry pigment, from which every trace of moisture has been removed by subjecting it to a temperature of 150° F. over night, and thirty-two parts by weight of poppyseed oil will make this color of the proper consistency after grinding to impalpable fineness in a stone mill of small diameter.
Ultramarine Green, while found in artists' color lists, is scarcely ever called for in picture or landscape painting, but has been used to some extent by decorators, because of its resistance to alkalies. In this connection the deep shades have had the preference and sixty-five parts by weight of the dry pigment and thirty-five parts of poppyseed oil are the proper proportion for mixing and grinding. It is not profitable to keep much of this color put up in tubes, as there is a tendency for the oil to separate from the pigment and become hard.
Zinc Green, also known as cobalt green or Rinmann's green, named after the Swedish chemist who originally discovered the compound, is valued highly by artists and decorators because absolutely permanent in all painting methods. It is a combination of cobalt and zinc and can be made by intimately mixing six parts by weight of carbonate of cobalt (or ten parts phosphate of cobalt), with thirty parts by weight of zinc oxide, grinding fine as possible and then subjecting the mixture to almost white heat. For a lighter shade, double this quantity of zinc oxide is used. To determine whether zinc green is of the quality and not simply a mixture of zinc chromate and Prussian blue (which latter is unfit for artists' and decorators' use), mix the suspected specimen with dilute hydrochloric acid in a test tube, when the genuine article will readily color the solution a deep pink. If held in the flame of a Bunsen burner with borax on a platinum wire, it should give a deep blue color. About seventy-eight parts by weight of the dry pigment with twenty-two parts of poppyseed oil is the proper proportion for mixing and the grinding should be done on a good stone mill of small diameter, not over twelve inches.
Green Lakes are an uncertain quantity in this line of colors, as unless they are made with alumina hydrate, they do not give the rich effect desired by decorators and when these pigments contain alumina hydrate, they liver so badly after being ground in oil, that in a few days the color will not squeeze out of the tube, besides a color that livers in oil is unfit for use, because it will scale in short order from where it has been fixed. However, decorators and scene painters in theatres have use for green lakes, both of the yellow and blueish type and prefer them put up in tubes of large and convenient size, and if the color grinder specifies that the pigment is to be free of alumina hydrate, the color maker can supply it by precipitating brilliant green on blanc fixe for the blueish toned lake and the same green with auramine or naphtol yellow, also on blanc fixe, for the lake of yellowish tone with the proper mordants. These lakes can be made sufficiently rich for the purpose and being used for interior decoration only, will have fair durability and will not show up yellow under gas or electric light. About seventy parts by weight of dry lake to thirty parts by weight of poppyseed oil will make the right consistency for these lakes. Green lakes of vegetable origin are practically obsolete.